Abstract: Matrix-entrapment is one of the major methods of enzyme-immobilization. In order to overcome its shortcomings, such as low amount of entrapment, low reactivity because of high polymer content and low diffusion, as well as irregular shaping, the entrapment of urease by crosslinked polyac-rylamide had been investigated and spherical immobilized urease had been prepared with following properities. High amount of immobilized enzyme (1 part of enzyme to 1 part of polymer) and about 50% relative activity of the immobilized urease. Reactivity towards urea hydrolysis was 120mg/ ml for two hours at 37℃. The stability of the immobilized urease was increased in comparison to the free urease. When stored at 4℃, the loss of initial activity was 8% after 66 days, 22% after 106 days and at 37℃ the loss was 18% after 11 days. The spherical shape of the beads improved the mechanical strength and enhanced the column velocity. No leakage of the immobilized urease could be detected. The above properties render the immobilized urease suitable for active material as artificial kidney.